A variety of guns for firing frangible, generally spherical projectiles are known in the art. Marking guns, (commonly referred to as paint ball guns) for example, use pressure from compressed gas such as nitrogen or carbon dioxide to fire a gelatinous capsule containing a marking material (usually paint). The capsule breaks on impact with a target dispersing the material thereby marking the target. A popular recreational use for marking guns is in "survival games," a kind of mock war where opposing sides attempt to seek out and "shoot" one another with paint balls. Paint ball guns have also been used to segregate cattle within a herd and for a variety of other marking purposes.
Paint balls fired from such guns may have a limited trajectory because of the flight characteristics imposed on them by the amount of force that can be applied and by the configuration of the bore. In some applications, restrictions may exist on the velocity with which the ball may be expelled from the barrel. Consequently, there is a need for a gun that can affect the trajectory of the paint ball by changing its flight characteristics through changes in the gun bore rather than by increases in force applied to the ball.
It is important to note that paint balls are relatively frangible. It is, therefore, necessary that the structure or method used to improve the trajectory of the paint ball does not cause premature rupture of the ball.